Unfastening prevention device

ABSTRACT

An object of the present invention is to provide an unfastening prevention device which has nothing projecting outside, and can prevent unfastening at either head or distal end of a bolt. 
     An unfastening prevention is attained by covering a cap ( 6, 16 ) to screwed up fastening means formed of a bolt ( 2 ) and a nut ( 3 ). In a groove ( 6   a,    16   a ) formed on an inner surface of the cap ( 6, 16 ) an outer periphery of a spring ring ( 8 ) is engaged, an inner periphery of the spring ring being engaged in a groove ( 7   a ) of a holder ( 7 ), restricting axial direction ( 2   a ) and resulting in slip out prevention. Even when a torque is given on the cap ( 6, 16 ), the cap idles, fastening condition does not change and unfastening prevention is attained.

TECHNICAL FIELD

This invention relates to an unfastening prevention device for fasteningmeans once screwed up by bolts and nuts etc.

BACKGROUND ART

Conventionally, fastening by bolts and nuts is widely known inmechanical fastening places such as fastening of a number plate to abumper of automobiles, fastening of a pole base plate to anchor nuts oranchor bolts, fastening in construction sites of iron towers orbuildings and fastening parts to railroads or some structures. Accordingto screw up fastenings, it is easy to increase or decrease the fasteningrigidity by adjusting fastening torque and it is also possible toreadjust the fastening rigidity after the fastening process has beencompleted if necessary. General tools such as spanners may be utilizedto screw up or release bolts and nuts for transmitting torque, and largefastening rigidity can be easily obtained by applying relatively smalltorque. On the fastened places, various proposed unfastening means maybe applied to keep the fastened condition long.

But recently, crimes such as breaking fastening places of number plates,iron towers for power transmission lines and connecting places of railroads are committed by somebody unknown. Fastening places using boltsand nuts are possible to keep stable and long lasting fastened state byapplying appropriate unfastening prevention means. But it is notpossible to prevent some body with malicious intent break and loosenfastening means using general tools.

The present applicant has proposed unfastening prevention devices eachof which is covered on a fastened place of bolt and nut and is notreleased by general tools in patent application 2000-148383 (patentpublication KOKAI 2001-330020) and patent application 2000-218455(patent publication KOKAI 2002-39146). In the former patent application2000-148383, a cylindrical cover member is fixed on a shank of a bolt bya pin. In the patent application 2000-218455, a cover member is fixed ona distal bolt shank projecting from a nut.

But according to the patent application 2000-148383, the pin projectsout of the cover member. According to the patent application2000-218455, it is only applicable at distal end of the bolt shank, andit is not possible to prevent unfastening at head of the bolt.

SUMMARY OF THE INVENTION

(Technical Problem to be solved by the Invention)

An object of the present invention is to provide an unfasteningprevention device which has nothing projecting outside, and can preventunfastening at either head or distal end of a bolt shank.

(Solution for the Problem)

The invention as claimed in claim 1 of the present invention is anunfastening prevention device attached to screwed up fastening meanscomprising:

a cap covering at least torque-receiving portion from axially one sideof the fastened parts and being provided with a groove on its innersurface and a widened part on its inner surface close to its opening endof which inner diameter gradually increases as it goes to the openingend;

a spring means biased outwardly so as to engage its outer periphery intothe groove formed on the inner surface of the cap, being able to slidealong the inner surface of the cap except for the groove area and beingable to decrease its diameter due to compression from outside by thewidened part and

a restriction means for the spring means axially restricting the springmeans to move.

According to the first invention, the unfastening prevention device isattached to a fastening place screwed up by a bolt and nut and providedwith cover (cap) means, spring means and restriction means. The covermeans covers at least torque-receiving portion, and is provided with agroove on its inner surface in which groove outer periphery of thespring means is engaged. The restriction means locates in the fasteningplace and restricts axial movement of the spring means. When the springmeans is restricted in the fastened parts, cover means is attached fromone axial side, and the cover means are hammered, the spring means isdecreased in its diameter, slides on the inner surface especially onwidened part near open end of the cover means, then meets with thegroove and its outer periphery is engaged in the groove. The cover meanstogether with restriction means prevents axial movement of the covermeans and a possible removal of the cover means from fastened parts.Since the cover means covers at least torque-receiving portion of thefastening means, it is impossible to give any torque on the fasteningmeans by a general tool, resulting in perfect unfastening prevention. Onthe outer surface of the cover means, there is no need to provide anyportion protruding outside at all. The restriction means may be composedas a groove on head of bolt or nut as well as on outer surface ofspacers so as to be able to engage the inner periphery of the springmeans. The spring means may be used as a washer adjusting its axialposition by another washer(s) or/and spacer(s), and its outer peripheryis engaged in the inner groove of the cover means.

Another invention 2 is characterized by that said cap means is or is notprovided with plural holes penetrating from outer surface to the grooveformed on the inner surface.

According to the second invention, since the holes penetrate from outersurface to the inner groove, pins of special tool pressed into the holesare able to press the spring means inwardly. Resulting from decrease indiameter of the spring means, the outer periphery of the spring means isforced out from the inner groove of the cover means, causing not torestrict axial movement of the cover means so as to release the covermeans from the fastened parts. After the removal of the cover means formthe fastened parts, getting loosen or adjusting the fastening rigidityby general tool become possible. When the cover means is removed fromthe fastened parts, it is possible to loosen or readjust fasteningcondition by common spanners or like tools. Also when all said holes areabolished, the cover may be called as a dead-lock fit type, which issuitable when the cover must not be unfastened by all means, and itsmanufacturing cost can be decreased.

Another invention 3 is characterized by that said unfastening preventiondevice comprising, first elastic body biasing whole inner surface of thespring means radial outwardly located inside of the spring meansrestricted by the restriction means.

According to the third invention, since the spring means is biased bythe first elastic body radial outwardly at the position of restrictionin the groove by the restriction means, the spring means is kept at acertain position and all the peripheral portion projects uniformly andcoaxially. When the cover means is put, the inner surface of the covermeans slides smoothly on the outer surface of the spring means andcauses uniform decrease of the spring means diameter.

Another invention 4 is characterized by that said second elastic bodydisposed between the fastened parts and cap means, and compressed whenthe cap means is set.

According to the forth invention, in case a fastened part, e.g. a numberplate vibrates, vibration and noise of cover means are prevented by thesecond elastic body, and when the cover means is released by specialtool, the cover means is popped out automatically.

(Effects over Prior Arts)

As described above, according to the present invention (first to forthinventions), the cover means is attached to a fastened place screwed upby a bolt and nut and the cover means covers at least torque-receivingportion. The cover means is not provided with anything projectedoutwardly. The cover is provided with a groove on its inner surface inwhich groove outer periphery of the spring means is engaged. Since oncecover means is attached, the axial movement of the cover means isrestricted by the spring means, cover means is prevented removing fromthe fastening place. Due to the presence of the cover means, it is notpossible to give unfastening torque using general tools resulting inunfastening prevention. The restriction means may be composed as agroove on head of bolt or nut as well as on outer surface of spacers soas to be able to engage the inner periphery of the spring means.

Further, according to the present invention, it is possible to releasethe cover means from the fastening place using holes formed on covermeans and a special tool. After the removal of the cover means form thefastening place, getting loosen or adjusting the fastening rigiditybecome possible. Also when all said holes are abolished, the cover maybe so called a dead-lock fit type, which is suitable when the cover mustnot be unfastened by all means, and its manufacturing cost can bedecreased.

Further, according to the present invention, since the cover means iskept coaxial, it slides and is fitted smoothly.

Further, according to the present invention, in case a fastened part,e.g. a number plate vibrates, vibration and noise of cover means areprevented by the second elastic body, and when the cover means isreleased by special tool, the cover means is popped out automatically.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is partially sectional vertical views showing first and secondaspects of unfastening prevention devices according to the presentinvention.

FIG. 2 shows a plan view and sectional vertical view of a cap of anembodiment of FIG. 1, a sectional vertical view of another embodimentcorresponding to FIG. 2( b) and a sectional vertical view of anotherembodiment corresponding to d-d section of FIG. 2( b).

FIG. 3 shows a plan view and front view of a holder shown in theembodiment of FIG. 1.

FIG. 4 is a plan view of a spring ring shown in the embodiment of FIG.1.

FIG. 5 shows plan views of rubber rings (first and second elasticbodies) in the embodiment of FIG. 1.

FIG. 6 is a front view of a bolt used in the 3rd embodiment of thepresent invention.

FIG. 7 is a front view of a bolt used in the 4th embodiment of thepresent invention.

FIG. 8 shows a plan view and front view of a bolt in the 5th embodimentof the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows schematic embodiments of unfastening prevention devicesaccording to the present invention. FIG. 1( a) shows first aspect of theembodiment, and FIG. 1( b) shows second aspect. In the followingdrawings, like elements have like numbers and thereby eliminateduplicate explanations.

As shown in FIG. 1( a), in the unfastening prevention device 1 which isfirst aspect embodiment of present invention, a fastening means (place)for fastened parts 4, 5 is composed by a bolt 2 and a nut 3, and a coverelement i.e. cap 6 covers a head 2 b of the bolt 2 from one (upper) endof axle line 2 a extending upper and lower directions of the bolt 2,i.e. from the side of proximal end of the bolt 2. Inner surface of thecap 6 (cover element or cover means) opens downwardly via a widened part6 c of which diameter increases as it goes down axially downwardly alongthe axle line 2 a to its one (lower) end (the widened part 6 being aquasi taper slightly projecting inwardly in ark as shown in the drawingor in perfect taper), and is closed at another (upper) end forming abottom 6 d. From the bottom 6 d, nothing projects outside (upper side)axially along the axle line 2 a. Once the cap 6 is fixed, a spanner orother general tool can not be approached and be actuated to thefastening torque receiving part, i.e. at least to the head 2 b of thebolt 2. The cap 6 in the drawing is provided with an annular groove 6 aon the inner surface. Between an outer surface of the cap 6 and groove 6a, there are provided plural, for example four pin insertion holes 6 bapart equal in circumferential direction. When cap 6 is fully covered onthe fastening means, groove 6 a of the cap 6 opposes to an annulargroove 7 a formed on an outer surface of a holder 7. The holder 7 isdisposed between head 2 b of the bolt 2 and an upper surface of thefastened part 4 as if it is a common metal washer, and is provided witha tapered part 7 c which functions as an introducing guide to securecentering posture of the widened part 6 c when the cap 6 is beingattached. Between groove 6 a of the cap 6 and groove 7 a of the holder7, there is a spring ring 8 (resilient material). Between an innersurface of the spring ring 8 and groove 7 a of the holder 7, an elasticrubber ring 9 (first elastic body) is disposed.

In case of unfastening once attached cap 6 at an attaching factory, anexclusive special tool 10 is disposed as shown in FIG. 1( a), each pin10 b of four nail arms 10 a is adjusted to enter the pin insertion hole6 b, diameter of the spring ring 8 is decreased by pins 10 b fromoutside caused by turning a manipulation part 10 c and the spring ring 8is pushed out inside the groove 6 a, thereby the cap 6 is automaticallypopped up by up to that time compressed elastic body 11 (second elasticbody).

As shown in FIG. 1( b), unfastening prevention device 11 as secondaspect embodiment of the present invention, a cap 16 is engaged fromdistal end 2 c of the bolt 2 under the condition that holder 7 isdisposed between lower surface of the fastened part 5 and nut 3. Aninner surface of the cap 16 is provided with an annular groove 16 a, andspring ring 8 is put between the groove 16 a and groove 7 a of theholder 7 to effect fastening of the cap 16, above which is the same asthe embodiment of FIG. 1( a). Cap 16 is also provided with same pininsertion holes 16 b as pin insertion holes 6 b of the cap 6. A bottomof the cap 16 in this embodiment is provided with a bolt insertion hole16 d through which distal end 2 c of the bolt 2 is inserted. Even whendistal end 2 c of the bolt 2 is entered in the bolt hole 16 d, distalend 2 c is designed not to protrude outside the hole along axle line 2a. When axial height of the cap 16 is increased, or distal end 2 c ofthe bolt 2 is shortened, cap 6 shown in FIG. 1( a) which is not providedwith bolt hole 16 d may be used instead of cap 16. Reference numeral 16c is a widened part.

As shown in FIG. 1, when the caps 6, 16 are engaged on the fasteningmeans, grooves 6 a, 16 a of the caps 6, 16 and groove 7 a of the holder7 are tightly connected by the spring ring 8, axial movement along axialline 2 a of the caps 6, 16 are prevented thereby caps 6, 16 can not betaken out. Even when some torque around the axle line 2 a is actuatedouter surface of the caps 6, 16, slipping occurs between grooves 6 a, 16a and outer surface of the spring ring 8 or between inner surface of thespring ring 8 and groove 7 a of the holder 7, causing the caps 6, 16 runidle, and the torque is prevented to reach to the holder 7. If sometorque is transmitted to the holder 7, it is not possible to transmittorque to head 2 b of the bole 2 or nut 3, unfastening of the fasteningmeans is effectively prevented. In the embodiments of FIG. 1,unfastening prevention is effected at one side, i.e. head 2 b of thebolt 2 or distal end 2 c, the unfastening prevention may be effected onboth sides.

FIG. 2, FIG. 3, FIG. 4 and FIG. 5 show the cap 6, holder 7, spring ring8 and rubber ring 9, elastic body 11 of FIG. 1( a) respectively. In FIG.2 and FIG. 3, (a) shows plan view and (b) shows sectional elevationview. FIG. 4 and FIG. 5 show plan views.

As shown in FIGS. 2( a), 2(b), cap 6 is generally cylindrical and madeof metal such as iron (ferrous material) and axially one side is openand other side is closed. In the inner surface close to the opening end,the annular groove 6 a is formed. Plural pin insertion holes 6 b areformed between the groove 6 a and outer surface at regularcircumferential intervals. The open end inner surface of the cap 6 isprovided with a taper (widened part 6 c) inner diameter of whichincreasing as it goes to the opening. In other words, since the innerdiameter of the widened part 6 c is largest at the open end, it iseasily covered on the outer periphery of the spring ring 8 when the cap6 is going to be covered. Under the condition that the outer peripheryof the spring ring 8 is covered by the opening part (widened part 6 c),when the bottom 6 d is hammered, the widened part 6 c slides on theouter periphery of the spring ring 8, then the outer diameter of thespring ring 8 is decreased and finally the spring ring 8 engages in thegroove 6 a. Outer periphery of the spring ring 8 engages in the groove 6a. When the spring ring 8 engages in the groove 6 a, pins 10 b (FIG. 1(a)) are pressed inside the pin insertion holes 6 b against the outersurface of the spring ring 8 causing decrease of the diameter of thespring ring 8 and disengage the spring ring 8 from the groove 6 a.

As shown in FIG. 2( c), the cap 6 has no holes like pin insertion holes6 b of FIG. 2( b) thereby making it as a complete lock up type. Thislock up type is suitable for a fastening means which is obliged not tobe unfastened by all means. This type is able to decrease themanufacturing cost as low as possible.

As shown in FIG. 2( b), outer surface (upper surface) of bottom 6 d ofthe cap 6 is provided with a shallow recession 6 e, round for example,in which recession 6 e a seal 20 with for example logo mark is attachedby means of both side adhesive tape. The seal is not able to be peeledoff even using nails, so durability of the seal increases.

Although the groove 6 a in FIG. 2( b) is annular, as shown in FIG. 2(d), intermittent grooves 6 a with short circumferential length disposedannularly at regular intervals and a spring ring 8 made of piano wirewith ark projections 8 b engaged in the grooves 6 a may be used.

As shown in FIG. 3, holder 7 is generally annular and made of metal suchas iron. The holder 7 is provided with groove 7 a on the outer surface,a central insertion hole 7 b to be inserted by shank of the bolt 2, andtapered part 7 c located at one end. Inner periphery of the spring ring8 is engaged in the groove 7 a. The spring ring 8 is designed to almostcompletely enter in the groove 7 a when outer surface is compressedradially inwardly. Namely, groove 7 a of the holder 7 functions as arestriction means to restrict the axial movement of the spring ring 8.When attachment of the cap 6 is completed, although widened part 6 c ofthe cap 6 abuts or opposes with a small clearance left against thetapered part 7 c, main object of the tapered part 7 c is to stabilizethe posture (keep centering position) of the cap 6 during the capattaching procedure.

As shown in FIG. 4, spring ring 8 is made of metal plate such as ironplate annually, and is provided with an opening 8 a, a cut part incircumference. Diameter of the spring ring 8 is shortened by compressionfrom radially outward positions (for example from four positions atregular intervals). Upon releasing the compression force, the springring 8 returns to its free condition. By widening the interval of theopening, inner periphery of spring ring 8 may be engaged in groove 7 aof the holder 7. Once engaged in the groove 7 a, interval of the opening8 a returns to its free condition.

As shown in FIG. 5( a), rubber ring 9 is a sample of flexible ring madeof elastic material. In the embodiments of FIG. 1( a) and FIG. 1( b),spring ring 8 is set after rubber ring 9 is set in groove 7 a of theholder. According to the existence of rubber ring 9, spring ring 8 isset in an accurate center thereby equal radial amount of the outerperipheral portion of spring ring 8 is kept projecting. When spring ring8 is compressed from outside and shrunk in diameter, rubber ring 9 isalso compressed and shrunk, leaving room to spring ring 8 fordeformation. Instead of rubber ring 9, other plastic elastomer ring mayor may not be used.

As an example, rubber like elastic body 11 is provided with a centralsmall hall 11 a, fixed on an inner surface of cap bottom 6 d by forexample both sides adhesive tape (not shown), kept slightly (for example0.8 mm) compressed condition after the completion of cap 6 mountingprocedure, urging the cap 6 upwardly thereby eliminating clearancebetween spring ring 8 and holder 7 and also preventing chattering andnoise caused by vibration of cap 6. If the elastic body 11 is made ofsoft silicon rubber, long and stable elasticity is secured. By selectingdiameter of small hole 11 a, reaction force from elastic body 11 to theset cap 6 is adjusted at most suitable value thereby improvemanufacturing efficiency. Among alternatives of elastic body 11, thinwave annular spring or plural dish shaped springs piled by turns may beemployed.

FIG. 6 shows a bolt 22 to be used in the third embodiment of the presentinvention. In this embodiment, bolt 22 is provided with a flange 22 d ina head 22 b integrally, and a groove 22 e farmed around the flange 22 drestricts spring ring 8 shown in FIG. 4. Namely, instead of usingseparate holder 7 of embodiment shown in FIG. 1, bolt 22 itself has afunction of restricting means to restrict spring ring 8. In this kind ofgroove 22 e of flange 22 d, spring ring 8 is engaged, a nut is threadedon distal end 22 c of the bolt 22, and cap 6 is attached on the bolthead 22 b same as first embodiment shown in FIG. 1( a) to formunfastening prevention means.

FIG. 7 shows a bolt 32 used in fourth embodiment of this invention. Topsurface center of head 32 b of the bolt 32 is provided with, forexample, a hexagonal hole 32 d through which torque may be applied tofasten or loosen by a hexagonal rod wrench. In this embodiment, a groove32 e directly formed on outer surface of head 32 d of the bolt 32restricts spring ring 8 shown in FIG. 4. Namely, same as the embodimentof FIG. 6, instead of using separate holder 7 of embodiment shown inFIG. 1, bolt 32 itself functions to restrict spring ring 8 and a nut isthreaded on distal end 32 c of the bolt 32, thereby attainingunfastening prevention by attaching cap 6, same as first embodimentshown in FIG. 1( a).

FIG. 8 shows a nut 43 used for the fifth embodiment of this invention.The nut 43 of this embodiment comprises a head 43 a and a hollow skirt43 b. Outer surface of the hollow skirt 43 b is provided with a groove43 c, in which spring ring 8 shown in FIG. 4 is engaged. According tothis construction, unfastening prevention is attained by covering thecap 16, same as second embodiment of FIG. 1( b). The idea of using nutas a restriction means can be utilized on the nut with flange by makinga groove on the flange.

Although in above embodiments, parts with peripheral groove forreceiving inner periphery of the spring ring 8 are used, a washer and aspacer may be piled to make an annular space corresponding to thegroove.

INDUSTRIAL APPLICABILITY

The present invention is applicable using bolts and nuts etc. inmechanical fastening places such as fastening of number plate to bumperof automobiles, fastening of pole base plate to anchor nuts or anchorbolts, fastening in construction sites of iron towers or buildings andfastening parts to railroads or some structures.

The claimed invention is:
 1. An unfastening prevention device attachableto a screwed up fastener, comprising: a cap covering at least atorque-receiving portion of the fastener axially from one side, the caphaving a groove on an inner surface and a widened part on a portion ofthe inner surface close to an open end, an inner diameter of the widenedpart gradually as it goes toward the open end; a spring biased outwardlyso as to engage an outer periphery thereof into the groove formed on theinner surface of the cap, the spring being able to slide along the innersurface of the cap except for an area of the groove and being able todecrease its diameter due to compression from outside by the widenedpart: a restriction device for the spring axially restricting movementof the spring; and a first elastic body located inside of the springrestricted by the restriction device, the first elastic body biasing aninner surface of the spring radially outward.
 2. The unfasteningprevention device as claimed in claim 1, wherein said cap is providedwith plural holes penetrating from an outer surface to the groove formedon the inner surface.
 3. The unfastening prevention device as claimed inclaim 1 further comprising a second elastic body disposed between thefastener and the cap, the second elastic body being compressed when thecap is set.